Turn Your House Into Noise Cancellation Headphones

[Bret Cahill]

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch. If it
draws a lot of power or when there is little outdoor noise it might be
desirable to turn it off or have it automatically turn off after 5
minutes and then back on as soon as the noise exceeds a threshold.

Noise cancellation should be cheaper than redoing the walls and in
some ways it might be an easier problem than headphones where the
distances involved are only a cm.

A few noisy zones might be tolerable as long as the locations of quiet
zones in a room could be moved and adjusted.


Bret Cahill

 

[Peter Webb]

"Bret Cahill" <Bret_E_Cahill@yahoo.com> wrote in message
news:6a20c7cf-42b5-42b2-93cb-e7d0773ffd4b@n12g2000yqh.googlegroups.com...

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch. If it
draws a lot of power or when there is little outdoor noise it might be
desirable to turn it off or have it automatically turn off after 5
minutes and then back on as soon as the noise exceeds a threshold.

Noise cancellation should be cheaper than redoing the walls and in
some ways it might be an easier problem than headphones where the
distances involved are only a cm.

Noise cancelling headphones largely work because:

a) the distances involved are only a cm. The headphone speaker subtracts the
ambient noise from the signal. The distance from speaker to eardrum must be
much less than the wavelength of the sound for this to work (or else the
phase will be out). As the distance increases, the lowest frequency that can
cancelled decreases, making them increasingly less effective.

b) The microphone which detects ambient is acoustically isolated from the
speaker such that feedback doesn't occur. This is easy with headphones, will
be very problematic with regular speakers.

A few noisy zones might be tolerable as long as the locations of quiet
zones in a room could be moved and adjusted.


Bret Cahill

 

In sci.physics Peter Webb <webbfamily@optusnetdiespamdie.com.au> wrote:

"Bret Cahill" <Bret_E_Cahill@yahoo.com> wrote in message
news:6a20c7cf-42b5-42b2-93cb-e7d0773ffd4b@n12g2000yqh.googlegroups.com...
There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch. If it
draws a lot of power or when there is little outdoor noise it might be
desirable to turn it off or have it automatically turn off after 5
minutes and then back on as soon as the noise exceeds a threshold.

Noise cancellation should be cheaper than redoing the walls and in
some ways it might be an easier problem than headphones where the
distances involved are only a cm.


Noise cancelling headphones largely work because:

a) the distances involved are only a cm. The headphone speaker subtracts the
ambient noise from the signal. The distance from speaker to eardrum must be
much less than the wavelength of the sound for this to work (or else the
phase will be out). As the distance increases, the lowest frequency that can
cancelled decreases, making them increasingly less effective.

b) The microphone which detects ambient is acoustically isolated from the
speaker such that feedback doesn't occur. This is easy with headphones, will
be very problematic with regular speakers.

Also they do nothing for the "felt" noise in a high noise environment.

One would be better off in checking on rebates for noise reduction
modifications which are often available for those living near airports but
seldom publicized.


--
Jim Pennino

Remove .spam.sux to reply.

 

[glen herrmannsfeldt]

In comp.dsp Bret Cahill <Bret_E_Cahill@yahoo.com> wrote:

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch. If it
draws a lot of power or when there is little outdoor noise it might be
desirable to turn it off or have it automatically turn off after 5
minutes and then back on as soon as the noise exceeds a threshold.

I have heard of using triple pane windows to reduce noise near
freeways. That might not be enough for jet fighters, though.

Noise cancellation should be cheaper than redoing the walls and in
some ways it might be an easier problem than headphones where the
distances involved are only a cm.

But the (wall) area is larger. I believe that takes drivers
(speakers) distributed along the walls, spaced depending on
the frequencies that need canceling and the amount of cancelation
required. But $5000 is a small part of the price of most houses,
so you could probably go somewhat more.

And, you could also use it as a sound system at the same time!

Extra DSP challenge, it has to send the right signal to each speaker
such that a reasonable stereo image is formed.

A few noisy zones might be tolerable as long as the locations of quiet
zones in a room could be moved and adjusted.

Have a computer follow each person around and adjust the cancelation
for those positions in the room where people are.

I have also heard about active concert hall reflection control
systems that make halls that are acoustically larger than the
actual size, or otherwise improve the acoustics. It seems that
the problems could be related.


-- glen

 

[glen herrmannsfeldt]

In comp.dsp Peter Webb <webbfamily@optusnetdiespamdie.com.au> wrote:
(snip)

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch.

(snip)

Noise cancelling headphones largely work because:

a) the distances involved are only a cm. The headphone speaker
subtracts the ambient noise from the signal. The distance from
speaker to eardrum must be much less than the wavelength of the
sound for this to work (or else the phase will be out).

I believe that isn't quite right. If you have a whole wall full
of canceling speakers, it should still be able to work.
But yes, one will only work over distances somewhat shorter
than one wavelength.

As the distance increases, the lowest frequency that can
cancelled decreases, making them increasingly less effective.

b) The microphone which detects ambient is acoustically isolated
from the speaker such that feedback doesn't occur. This is easy
with headphones, will be very problematic with regular speakers.

I don't believe that this is true for headphones. As far as
I understand it, they have to correct for, and subtract, the
feedback.

-- glen

 

[CWatters]

On 15/09/2011 03:14, Peter Webb wrote:

"Bret Cahill" <Bret_E_Cahill@yahoo.com> wrote in message
news:6a20c7cf-42b5-42b2-93cb-e7d0773ffd4b@n12g2000yqh.googlegroups.com...
There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch. If it
draws a lot of power or when there is little outdoor noise it might be
desirable to turn it off or have it automatically turn off after 5
minutes and then back on as soon as the noise exceeds a threshold.

Noise cancellation should be cheaper than redoing the walls and in
some ways it might be an easier problem than headphones where the
distances involved are only a cm.


Noise cancelling headphones largely work because:

a) the distances involved are only a cm. The headphone speaker subtracts
the ambient noise from the signal. The distance from speaker to eardrum
must be much less than the wavelength of the sound for this to work (or
else the phase will be out). As the distance increases, the lowest
frequency that can cancelled decreases, making them increasingly less
effective.

b) The microphone which detects ambient is acoustically isolated from
the speaker such that feedback doesn't occur. This is easy with
headphones, will be very problematic with regular speakers.

c) It's hard to make destructive interference occur everywhere in a
large volume.

Consider..If you have three people in a room you need to create
destructive interference in six places (each ear) and they are moving
virtually independantly. Can't imagine how it can be done without
headphones.

 

[Rui Maciel]

Bret Cahill wrote:

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch.

If residents are willing to pay that kind of cash to lower the ambient noise
levels in their homes then all they need to do is soundproof them.
Insulating the walls does just that and it also brings the added benefit of
reducing the energy spent in HVAC. Adding sound reflection panels also
helps, with the added benefit of being able to provide some shade. None of
these technologies require an increase in energy spending.


Rui Maciel

 

[Jerry Avins]

On 9/15/2011 11:45 AM, Bret Cahill wrote:

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch. If it
draws a lot of power or when there is little outdoor noise it might be
desirable to turn it off or have it automatically turn off after 5
minutes and then back on as soon as the noise exceeds a threshold.

Noise cancellation should be cheaper than redoing the walls and in
some ways it might be an easier problem than headphones where the
distances involved are only a cm.

Noise cancelling headphones largely work because:

a) the distances involved are only a cm. The headphone speaker subtracts
the ambient noise from the signal. The distance from speaker to eardrum
must be much less than the wavelength of the sound for this to work (or
else the phase will be out). As the distance increases, the lowest
frequency that can cancelled decreases, making them increasingly less
effective.

b) The microphone which detects ambient is acoustically isolated from
the speaker such that feedback doesn't occur. This is easy with
headphones, will be very problematic with regular speakers.

c) It's hard to make destructive interference occur everywhere in a
large volume.

It need not be everywhere or even most areas of the room.

It needs to be done for each ear separately, for all individuals in the
room as they move around. The cancelling signal for one ear must not add
to the noise at another. I don't see it happening.

Consider..If you have three people in a room you need to create
destructive interference in six places (each ear) and they are moving
virtually independantly. Can't imagine how it can be done without
headphones.

The system could monitor the location of the head of each person in
the room. GPS isn't quite there yet so it must be done locally, with
sonar or radar using a target much less cumbersome than headphones,
i.e., an ear ring, cap or necklace.

The signals from the speakers would be coordinated to eliminate just
the noise in a small 0.03 m^3 volume around each head.

Around each _ear_ simultaneously.

This approach requires a more sophistication in the design but would
greatly reduce the cost and power and the number and/or size of the
speakers for the production run.

What production run?

If you could do this, you could also build a system that allowed you to
listen to a symphony, while the person sitting at the other end of a
couch heard rock and roll. I doubt it!

Jerry
--
Engineering is the art of making what you want from things you can get.

 

[Vladimir Vassilevsky]

davew wrote:

Active "wallpaper" with hundreds or even thousands of small speakers
in a massive array with precise multiple beamforming capability should
be able to do the job. I wouldn't be surprised if this hasn't already
been done in military projects to acoustically cloak submarines/boat
hulls.

The ANC systems for cars were proposed while ago. Those systems are
trying to cancel noise at the locations of the heads of the driver and
the passengers. Somewhat 10dB of improvement is possible, however the
advantage does not outweigth complexity and cost.

The active mufflers for engine exaust pipe were tried, too. It works,
but why bother if the same result could be accomplished by traditional
means.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

 

[Marvin the Martian]

On Wed, 14 Sep 2011 16:04:09 -0700, Bret Cahill wrote:

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able to
talk to other people in a room at the flip of a switch. If it draws a
lot of power or when there is little outdoor noise it might be desirable
to turn it off or have it automatically turn off after 5 minutes and
then back on as soon as the noise exceeds a threshold.

Noise cancellation should be cheaper than redoing the walls and in some
ways it might be an easier problem than headphones where the distances
involved are only a cm.

A few noisy zones might be tolerable as long as the locations of quiet
zones in a room could be moved and adjusted.


Bret Cahill

Simple noise cancellation headphones work by picking up the ambient noise
and then reproducing it 180 degrees out of phase. It works in the
immediate vicinity, for wavelengths that are long enough. Sadly, for loud
noise, coving the ears is insufficient; you have to cover the head as
well.

To do a whole room you'd need a Bessel array of microphones and speakers,
and some rather sophisticated real time microprocessors.

I worked on this years ago... maybe with the new ARM microprocessors, I
should look at it again. Probably doing this is a lot cheaper now.

Sadly, I got pushed out of my audio job because I lost a lot of my
hearing and I'm not a blond bimbo with big tits who suck on managers who
think that there is nothing to audio engineering than matching plugs to
microphone connectors. I was quite good at this.

 

[Bret Cahill]

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch. If it
draws a lot of power or when there is little outdoor noise it might be
desirable to turn it off or have it automatically turn off after 5
minutes and then back on as soon as the noise exceeds a threshold.

Noise cancellation should be cheaper than redoing the walls and in
some ways it might be an easier problem than headphones where the
distances involved are only a cm.

Noise cancelling headphones largely work because:

a) the distances involved are only a cm. The headphone speaker subtracts
the ambient noise from the signal. The distance from speaker to eardrum
must be much less than the wavelength of the sound for this to work (or
else the phase will be out). As the distance increases, the lowest
frequency that can cancelled decreases, making them increasingly less
effective.

b) The microphone which detects ambient is acoustically isolated from
the speaker such that feedback doesn't occur. This is easy with
headphones, will be very problematic with regular speakers.

c) It's hard to make destructive interference occur everywhere in a
large volume.

It need not be everywhere or even most areas of the room.

Consider..If you have three people in a room you need to create
destructive interference in six places (each ear) and they are moving
virtually independantly. Can't imagine how it can be done without
headphones.

The system could monitor the location of the head of each person in
the room. GPS isn't quite there yet so it must be done locally, with
sonar or radar using a target much less cumbersome than headphones,
i.e., an ear ring, cap or necklace.

The signals from the speakers would be coordinated to eliminate just
the noise in a small 0.03 m^3 volume around each head.

This approach requires a more sophistication in the design but would
greatly reduce the cost and power and the number and/or size of the
speakers for the production run.


Bret Cahill

 

[Marvin the Martian]

On Thu, 15 Sep 2011 09:25:51 +0100, CWatters wrote:

On 15/09/2011 03:14, Peter Webb wrote:

"Bret Cahill" <Bret_E_Cahill@yahoo.com> wrote in message
news:6a20c7cf-42b5-42b2-93cb-
e7d0773ffd4b@n12g2000yqh.googlegroups.com...
There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch. If it draws
a lot of power or when there is little outdoor noise it might be
desirable to turn it off or have it automatically turn off after 5
minutes and then back on as soon as the noise exceeds a threshold.

Noise cancellation should be cheaper than redoing the walls and in
some ways it might be an easier problem than headphones where the
distances involved are only a cm.


Noise cancelling headphones largely work because:

a) the distances involved are only a cm. The headphone speaker
subtracts the ambient noise from the signal. The distance from speaker
to eardrum must be much less than the wavelength of the sound for this
to work (or else the phase will be out). As the distance increases, the
lowest frequency that can cancelled decreases, making them increasingly
less effective.

b) The microphone which detects ambient is acoustically isolated from
the speaker such that feedback doesn't occur. This is easy with
headphones, will be very problematic with regular speakers.

c) It's hard to make destructive interference occur everywhere in a
large volume.

Consider..If you have three people in a room you need to create
destructive interference in six places (each ear) and they are moving
virtually independantly. Can't imagine how it can be done without
headphones.

That's why you use the Bessel array. The noise is coming from far away,
but the noise canceling sound is coming from much closer. You have to
make the noise canceling sound appear to be coming from the noise source
point. You can do this with a Bessel array.

 

[Marvin the Martian]

On Thu, 15 Sep 2011 08:45:08 -0700, Bret Cahill wrote:

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch. If it
draws a lot of power or when there is little outdoor noise it might
be desirable to turn it off or have it automatically turn off after
5 minutes and then back on as soon as the noise exceeds a threshold.

Noise cancellation should be cheaper than redoing the walls and in
some ways it might be an easier problem than headphones where the
distances involved are only a cm.

Noise cancelling headphones largely work because:

a) the distances involved are only a cm. The headphone speaker
subtracts the ambient noise from the signal. The distance from
speaker to eardrum must be much less than the wavelength of the sound
for this to work (or else the phase will be out). As the distance
increases, the lowest frequency that can cancelled decreases, making
them increasingly less effective.

b) The microphone which detects ambient is acoustically isolated from
the speaker such that feedback doesn't occur. This is easy with
headphones, will be very problematic with regular speakers.

c) It's hard to make destructive interference occur everywhere in a
large volume.

It need not be everywhere or even most areas of the room.

Consider..If you have three people in a room you need to create
destructive interference in six places (each ear) and they are moving
virtually independantly. Can't imagine how it can be done without
headphones.

The system could monitor the location of the head of each person in the
room. GPS isn't quite there yet so it must be done locally, with sonar
or radar using a target much less cumbersome than headphones, i.e., an
ear ring, cap or necklace.

Easier to eliminate the noise in the room, and such a system would be
dangerous, as the sound intensity would likely be, at times, quite loud
in certain local areas.

The signals from the speakers would be coordinated to eliminate just the
noise in a small 0.03 m^3 volume around each head.

Or, you could use the system to pop their heads.

This approach requires a more sophistication in the design but would
greatly reduce the cost and power and the number and/or size of the
speakers for the production run.

Power is really not a problem. Couple of pre-Obama light bulbs' worth.

 

[Marvin the Martian]

On Thu, 15 Sep 2011 09:50:25 -0700, davew wrote:

On Sep 15, 4:45 pm, Bret Cahill <Bret_E_Cah...@yahoo.com> wrote:
There is some otherwise nice real estate at the end of Navy
runways, neighborhoods in San Diego and Virginia Beach where
pilots practice taking off an aircraft carrier with after burners
wide open.

A lot of residents would be willing to pay $5,000 or more to be
able to talk to other people in a room at the flip of a switch. If
it draws a lot of power or when there is little outdoor noise it
might be desirable to turn it off or have it automatically turn
off after 5 minutes and then back on as soon as the noise exceeds
a threshold.

Noise cancellation should be cheaper than redoing the walls and in
some ways it might be an easier problem than headphones where the
distances involved are only a cm.

Noise cancelling headphones largely work because:

a) the distances involved are only a cm. The headphone speaker
subtracts the ambient noise from the signal. The distance from
speaker to eardrum must be much less than the wavelength of the
sound for this to work (or else the phase will be out). As the
distance increases, the lowest frequency that can cancelled
decreases, making them increasingly less effective.

b) The microphone which detects ambient is acoustically isolated
from the speaker such that feedback doesn't occur. This is easy
with headphones, will be very problematic with regular speakers.

c) It's hard to make destructive interference occur everywhere in a
large volume.

It need not be everywhere or even most areas of the room.

Consider..If you have three people in a room you need to create
destructive interference in six places (each ear) and they are moving
virtually independantly. Can't imagine how it can be done without
headphones.

The system could monitor the location of the head of each person in the
room.  GPS isn't quite there yet so it must be done locally, with sonar
or radar using a target much less cumbersome than headphones, i.e., an
ear ring, cap or necklace.

The signals from the speakers would be coordinated to eliminate just
the noise in a small 0.03 m^3 volume around each head.

This approach requires a more sophistication in the design but would
greatly reduce the cost and power and the number and/or size of the
speakers for the production run.

Bret Cahill- Hide quoted text -

- Show quoted text -

Active "wallpaper" with hundreds or even thousands of small speakers in
a massive array with precise multiple beamforming capability should be
able to do the job. I wouldn't be surprised if this hasn't already been
done in military projects to acoustically cloak submarines/boat hulls.

You only need speakers that are spaced about 1/2 the highest wavelength
of the highest frequency you want to cancel.

And you don't form a beam (though you could...) you make it look like the
canceling sound is coming from the same point in space as the noise.

 

[Bret Cahill]

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch.

If residents are willing to pay that kind of cash to lower the ambient noise
levels in their homes then all they need to do is soundproof them.  

This was for a normal looking house, large glass windows, etc. The
cheapest passive way to reduce the low frequency noise from an
afterburner 150' above to a level that allows conversation is to dig a
bunker which is difficult to keep submerged in Va. Beach.

Also a lot of people rent their homes. They can always sell the
system when they move.

Insulating the walls does just that and it also brings the added benefit of
reducing the energy spent in HVAC.  Adding sound reflection panels also
helps, with the added benefit of being able to provide some shade.  None of
these technologies require an increase in energy spending.

The father of a concert symphony music composer worked on noise
reduction at NASA. He never was successful according to his kid.


Bret Cahill

 

[Marvin the Martian]

On Thu, 15 Sep 2011 10:10:54 -0700, Bret Cahill wrote:

If they can get motorcyclists to trade in their pipes for something that
makes them look like a semi-rig, an outdoor noise issue could be solved.

Harleys make noise on purpose. I think it makes them safer (unless you
consider the hearing losses involved).

When I hear a Harley I look around to see where it is. Now a BMW bike,
those damned things are quiet and you don't seem 'em until the bike rider
(almost universally a jackass with a short expected life span) until they
already done something stupid. You see the idiot on the Harley before he
does something stupid.

 

[davew]

On Sep 15, 4:45 pm, Bret Cahill <Bret_E_Cah...@yahoo.com> wrote:

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch. If it
draws a lot of power or when there is little outdoor noise it might be
desirable to turn it off or have it automatically turn off after 5
minutes and then back on as soon as the noise exceeds a threshold.

Noise cancellation should be cheaper than redoing the walls and in
some ways it might be an easier problem than headphones where the
distances involved are only a cm.

Noise cancelling headphones largely work because:

a) the distances involved are only a cm. The headphone speaker subtracts
the ambient noise from the signal. The distance from speaker to eardrum
must be much less than the wavelength of the sound for this to work (or
else the phase will be out). As the distance increases, the lowest
frequency that can cancelled decreases, making them increasingly less
effective.

b) The microphone which detects ambient is acoustically isolated from
the speaker such that feedback doesn't occur. This is easy with
headphones, will be very problematic with regular speakers.

c) It's hard to make destructive interference occur everywhere in a
large volume.

It need not be everywhere or even most areas of the room.

Consider..If you have three people in a room you need to create
destructive interference in six places (each ear) and they are moving
virtually independantly. Can't imagine how it can be done without
headphones.

The system could monitor the location of the head of each person in
the room.  GPS isn't quite there yet so it must be done locally, with
sonar or radar using a target much less cumbersome than headphones,
i.e., an ear ring, cap or necklace.

The signals from the speakers would be coordinated to eliminate just
the noise in a small 0.03 m^3 volume around each head.

This approach requires a more sophistication in the design but would
greatly reduce the cost and power and the number and/or size of the
speakers for the production run.

Bret Cahill- Hide quoted text -

- Show quoted text -

Active "wallpaper" with hundreds or even thousands of small speakers
in a massive array with precise multiple beamforming capability should
be able to do the job. I wouldn't be surprised if this hasn't already
been done in military projects to acoustically cloak submarines/boat
hulls.

 

[glen herrmannsfeldt]

In comp.dsp Rui Maciel <rui.maciel@gmail.com> wrote:

Bret Cahill wrote:

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch.

If residents are willing to pay that kind of cash to lower the
ambient noise levels in their homes then all they need to do
is soundproof them.

But then you don't learn anything about new applications for
DSP technology.

Insulating the walls does just that and it also brings the added
benefit of reducing the energy spent in HVAC.

San Diego has a pretty moderate climate, so HVAC cost should already
be pretty low. Virginia Beach may be different.

Adding sound reflection panels also helps, with the added benefit
of being able to provide some shade. None of these technologies
require an increase in energy spending.

The next problem is diffraction. Sound reflection is fine, but
the low frequencies will diffract around the edge. I will guess
that jet fighters with afterburners make a lot of low frequencies.
Low frequencies are also harder to absorb inside the walls.

Now, if someone proposed this as a research project it might be
that someone would fund it. Use all the technologies: sound
reflection, sound absorption, and active cancelation in one house.

-- glen

 

[Bret Cahill]

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch. If it
draws a lot of power or when there is little outdoor noise it might be
desirable to turn it off or have it automatically turn off after 5
minutes and then back on as soon as the noise exceeds a threshold.

Noise cancellation should be cheaper than redoing the walls and in
some ways it might be an easier problem than headphones where the
distances involved are only a cm.

Noise cancelling headphones largely work because:

a) the distances involved are only a cm. The headphone speaker subtracts
the ambient noise from the signal. The distance from speaker to eardrum
must be much less than the wavelength of the sound for this to work (or
else the phase will be out). As the distance increases, the lowest
frequency that can cancelled decreases, making them increasingly less
effective.

b) The microphone which detects ambient is acoustically isolated from
the speaker such that feedback doesn't occur. This is easy with
headphones, will be very problematic with regular speakers.

c) It's hard to make destructive interference occur everywhere in a
large volume.

It need not be everywhere or even most areas of the room.

Consider..If you have three people in a room you need to create
destructive interference in six places (each ear) and they are moving
virtually independantly. Can't imagine how it can be done without
headphones.

The system could monitor the location of the head of each person in
the room.  GPS isn't quite there yet so it must be done locally, with
sonar or radar using a target much less cumbersome than headphones,
i.e., an ear ring, cap or necklace.

The signals from the speakers would be coordinated to eliminate just
the noise in a small 0.03 m^3 volume around each head.

This approach requires a more sophistication in the design but would
greatly reduce the cost and power and the number and/or size of the
speakers for the production run.

Bret Cahill- Hide quoted text -

- Show quoted text -

Active "wallpaper" with hundreds or even thousands of small speakers
in a massive array with precise multiple beamforming capability should
be able to do the job.  

How are holograms done?

If they can get motorcyclists to trade in their pipes for something
that makes them look like a semi-rig, an outdoor noise issue could be
solved.

I wouldn't be surprised if this hasn't already
been done in military projects to acoustically cloak submarines/boat
hulls.

Inside out instead of outside in?


Bret Cahill

 

[Jerry Avins]

On 9/15/2011 2:02 PM, Marvin the Martian wrote:

...

You only need speakers that are spaced about 1/2 the highest wavelength
of the highest frequency you want to cancel.

Highest wavelength of the highest frequency? At any one frequency, there
is only one wavelength. Did you mean, "wavelength of the highest
frequency"? Let's see: sound travels about 1100 ft/sec in air, and 10
KHz is a low end for decent cancellation. 1.1/10 gives a wavelength of
..11 ft, and half of that is .055 ft or .66 in. What qualifies as "only"?

And you don't form a beam (though you could...) you make it look like the
canceling sound is coming from the same point in space as the noise.

Good trick! How?

Jerry
--
Engineering is the art of making what you want from things you can get.